1. Technical Field
The present invention relates to an interface device and an information processing system provided therewith. The interface device establishes an interface between a CPU and an external unit such as a PC card.
2. Background Arts
As one kind of external units of a computer, there is known a card of the PCMCIA (Personal Computer Memory Card International Association) standard (hereinafter referred to as a PC card). As examples of the PC card, there are given a memory card incorporating a memory therein and various kinds of I/O cards which function as input/output interfaces. Further examples of such I/O cards include a modem card and a SCSI card.
As one of various kinds of signals outputted from such PC cards there is a wait signal (WAIT). The PC card functions such that it asserts such wait signal in the case that the bus cycle is desired to be extended by delaying the termination of the access cycle when it is accessed by CPU and the like.
However, it is usual that when the PC card asserts a wait signal, the PC card occupies the bus of the system during the assertion. Therefore, where the PC card continues to assert the wait signal due to a failure or other reasons, the bus of the system is kept occupied by the PC card. As a result, the system becomes frozen.